The long-term goal of these studies is to better understand cell division in the model organism Escherichia coli. A deeper understanding of bacterial cell division is expected to facilitate the development of new antibiotics and will therefore benefit public health. In E. coli, cell division is mediated by a structure called the septal ring, which is known to contain about 20 proteins. An important challenge for the future will be to identify and characterize any proteins that are missing from the current model. The experiments proposed here concern three newly discovered E. coli septal ring proteins that carry a peptidoglycan binding domain known as a SPOR domain. Specific Aim1 will explore the roles of the SPOR domain proteins during constriction. Specific Aims 2 and 3 are based on the observation that the SPOR domains themselves localize to the division site. This implies that SPOR domains bind preferentially to septal peptidoglycan. Aim 2 explores structural features of peptidoglycan that are recognized by SPOR domains. Aim 3 defines the structure of the peptidoglycan binding site on a SPOR domain. Understanding how SPOR domains specifically target septal peptidoglycan might provide important insights into septal peptidoglycan synthesis. PUBLIC HEALTH RELEVANCE: The studies proposed here will lead to a greater understanding of bacterial cell division. That knowledge can be used to develop new antibiotics.